Structural,optical, and photoelectrochemical properties of nanosphere-like CdXZn1-XS synthesized by electrochemical route

Here, we present the effect of different Zn contents on the structural, morphological, and optical properties of Cd_XZn_1-XS thin films deposited by electrodeposition method on stainless steel and indium-doped tin oxide (ITO) glass substrates. Electrosynthesized Cd_XZn_1-XS thin films are characterized by using X-ray diffraction (XRD), UV-Vis spectrophotometer, field emission scanning electron microscope (FE-SEM), and surface wettability analysis. XRD pattern reveals that the Cd_XZn_1-XS thin films are polycrystalline in nature with hexagonal crystal structure. FE-SEM micrograph displays that these Cd_XZn_1-XS thin films exhibit the different sizes of sphere-like nanostructures by varying the X value. The optical absorption study indicates that drastic variation in band gap energy of Cd_XZn_1-XS thin films. In advance photovoltaic measurements, Cd_XZn_1-XS thin films are to be studied by forming the photoelectrochemical (PEC) cell having Cd_XZn_1-XS/0.5 M (Na₂SO₃)/C configuration. The efficiency values of Cd_XZn_1-XS are found to be 0.2, 0.35, 0.32, 0.25, and 0.23 % respectively at X content.

     

Structure, refractive-index dispersion and the optical absorption edge of chemically deposited ZnxCd(1-x)S thin films

Zinc cadmium sulfide, Zn_xCd_(1-x)S, thin films have been deposited by a simple and inexpensive chemical bath deposition method from an aqueous medium using thiourea as a sulfide-ion source. The structure of the deposited films has been characterized by X-ray diffraction and transmission electron microscopy. It was observed from X-ray diffraction that the as-deposited films were amorphous in nature. However Zn_xCd_(1-x)S films annealed at 423 K for 1.5 h show a crystalline structure with a small scattering volume. The obtained results were confirmed throughout the transmission electron microscopy and the corresponding electron-diffraction patterns. The optical constants of Zn_xCd_(1-x)S films annealed at 423 K for 1.5 h in the compositional range 0≤x≤1 were estimated using transmission and reflection spectra in the wavelength range 300–2500 nm. The band gap varies non-linearly with the value of x. The dependence of the refractive index on the wavelength obeys the single-oscillation model, from which the dispersion parameters and the high-frequency dielectric constant were determined. A graphical representation of the surface and volume energy-loss functions was also given. Received: 23 February 2001 / Accepted: 26 February 2001 / Published online: 27 June 2001     

Investigation on the structural properties and correlation of the optical constants of Cd1-xZnxS thin films with bath deposition temperature

Cd_1-xZn_xS thin films were deposited by chemical bath deposition (CBD) technique, which is simple and cost effective, in a chemical bath containing appropriate amount of cadmium acetate, zinc acetate, and thiourea as precursors, in a clean glass substrate. The deposition was carried out by varying the bath temperatures (70 °C, 75 °C, 80 °C, and 85 °C) of the precursor solution. The XRD results indicate the existence of hexagonal structures of Cd_1-xZn_xS with an average crystallite size of ∼ 27–41 nm. EDX studies confirm the presence of Cd, Zn, and S in the films. HRTEM and SAED patterns show the crystalline nature of the films with the coexistence of the hexagonal phase. The optical constants viz; optical band gap, Urbach energy, static refractive index, and optical conductivity were studied by using UV- Vis transmission spectra as a function of CBD temperature. It was observed that with the increase of bath temperature in the above range, there were concomitant decreases in optical band gap from ∼3.3 to 2.8 eV. The Urbach energy, optical conductivity, and static refractive index of the films increase with the increase in bath deposition temperature. FTIR studies confirm the formation of ternary Cd_1-xZn_xS thin films.     

The optical properties of CdxZn1−xS thin films on glass substrate prepared by spray pyrolysis method

A series of Cd_xZn_1−xS thin films have been deposited on glass substrates using spray pyrolysis technique. The crystallinity and microstructure of Cd_xZn_1−xS thin films have been investigated by X-ray diffraction (XRD). Based on the results of Hall measurements, the films obtained were an n-type semiconductor. The X-ray data analysis of Cd_xZn_1−xS thin films showed that the grain size of the Cd_xZn_1−xS increased with increase in Cd composition. It is observed that the band gap increases as the Cd composition decreases. The results also showed a blue shift of absorption edge of optical transmission spectra is increases as Zn ratio increases. The effects of Cd composition on the structural and optical properties of Cd_xZn_1−xS thin films were related to their grain size, stress and carrier concentration.     

Effect of NaF on optical and structural properties of CdxZn1−xS nano crystalline films

This work investigates the effect of NaF on optical and structural properties of nano crystalline Cd_xZn_1?xS films. The Cd_xZn_1?xS films are prepared through chemical bath deposition (CBD) technique in aqueous alkaline bath and their subsequent condensation on substrates. The as-obtained samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–VIS absorption spectroscopy. Micro structural features, obtained from XRD analysis confirm the formation of cubic phase of undoped as well as NaF doped Cd_xZn_1?xS nano particles while SEM observations depict non-uniform distribution of grains. These results show the average grain size of pure as well as NaF doped samples to range from 50 to 90 nm. Tauc's plots, extracted from absorption spectra exhibit absorption to be dominating mainly in blue-green region of visible spectrum. The room-temperature photoluminescence (PL) spectra of Cd_xZn_1?xS samples show a peak around 425 nm, which gets blue shifted for doped sample indicating improvement in PL properties on its addition.     

Blue-violet luminescence double peak of In-doped films prepared by radio frequency sputtering

ZnO films doped with different contents of indium were prepared by radio frequency sputtering technique. The structural, optical and emission properties of the films were characterized at room temperature using XRD, XPS, UV-vis-NIR and PL techniques. Results showed that the indium was successfully incorporated into the c-axis preferred orientated ZnO films, and the In-doped ZnO films are of over 80% optical transparency in the visible range. Furthermore, a double peak of blue-violet emission with a constant energy interval (∼0.17 eV) was observed in the PL spectra of the samples with area ratio of indium chips to the Zn target larger than 2.0%. The blue peak comes from the electron transition from the Zn_i level to the top of the valence band and the violet peak from the In_Zn donor level to the V_Zn level, respectively.     

Structural,electrical and optical properties of Cd1−xZnxO thin films and alloying effects on Kβ/Kα intensity ratios

Cd_1?xZn_xO thin films were prepared by spray pyrolysis in air atmosphere on a glass substrate at 250 °C. The Zn content in Cd_1?xZn_xO films was varied from x = 0 to 0.60. Structural, electrical and optical properties of Cd_1?xZn_xO films were investigated by x‐ray diffraction, electrical resistivity and optical transmittance spectra, respectively. As the Zn content in Cd_1?xZn_xO thin films increased, the preferred orientation of the films did not change, only the peak intensity of the planes decreased. In addition to the peaks of CdO, peaks of ZnO were observed in the film with x = 0.6. The resistivity of Cd_1?xZn_xO thin films increased with increasing Zn content. Transmittance spectra studies of films were carried out in the 190‐1100 nm wavelength range and the results showed that the bandgap energy range varied from 2.42 to 3.25 eV. In addition, alloying effect on the Kβ/Kα intensity ratio in Cd_1?xZn_xO semiconductor thin films was studied. It was found that the Kβ/Kα intensity ratio is changed by alloying effects in Cd_1?xZn_xO semiconductor thin films for different composition of x. The results were compared with the theoretical values. Copyright © 2006 John Wiley & Sons, Ltd.     

Electronic and optical properties of CdS/CdZnS nanocrystals

Cd1-x ZnxS nanocrystals are prepared by a co-precipitation method with different atomic fractions of Zn.The texture,structural transformation and optical properties with increasing x value in Cd1-x ZnxS are studied with scanning electron microscopy,electron diffraction patterning,and absorption spectra respectively.Quantum confinement in a strained CdS/Cd1-xZnxS related nanodot with various Zn content values is investigated theoretically.Binding energies on exciton bound CdS/CdxZn1-xS quantum dot are computed,with consideration of the internal electric field induced by the spontaneous and piezoelectric polarizations,and thereby the interband emission energy is calculated as a function of the dot radius.The optical band gap from the UV absorption spectrum is compared with the interband emission energy computed theoretically.Our results show that the average diameter of composite nanoparticles ranges from 3 nm to 6 nm.The X-ray diffraction pattern shows that all the peaks shift towards the higher diffracting angles with an increase in Zn content.The lattice constant gradually decreases as the Zn content increases.The strong absorption edge shifts towards the lower wavelength region and hence the band gap of the films increases as the Zn content increases.The values of the absorption edge are found to shift towards the shorter wave length region and hence the direct band gap energy varies from 2.5 eV for the CdS film and 3.5 eV for the ZnS film.Our numerical results are in good agreement with the experimental results.     

Effect of indium doping on photoelectrochemical properties of Cd0.9Zn0.1Se photosensitive films

Indium doped Cd_0.9Zn_0.1Se films have been synthesized by chemical bath deposition method. The deposited films act as photoanode in photoelectrochemical (PEC) cells. The varying concentration of indium from 0.01 to 1.0 mol% was used. The film thickness increases from 0.72 to 0.80 μm as doping concentration increases up to 0.1 mol%, thereafter it decreases. The cell configuration is n-Cd_0.9Zn_0.1Se:In|NaOH (1 M)+S (1 M)+Na₂S (1 M)|C_(graphite). The various performance parameters were examined with respect to doping concentration of indium. It is found that fill factor and efficiency is maximum for 0.1 mol% indium photosensitive films. This is due to low resistance, high flat band potential, maximum open circuit voltage as well as maximum short-circuit current. The barrier height was examined from the temperature dependence of the reverse saturation current. The lighted ideality factor was found to be minimum for 0.1 mol% indium photosensitive films. A cell utilizing doping photosensitive films showed a wider spectral response. The utility of this work is in improving efficiency of the PEC cell.     

Annealing effect on the structural and optical properties of a Cd1−xZnxS thin film for photovoltaic applications

Herein is a report of a study on a Cd_1−xZn_xS thin film grown on an ITO substrate using a chemical bath deposition technique. The as-deposited films were annealed in air at 400 °C for 30 min. The composition, surface morphology and structural properties of the as-deposited and annealed Cd_1−xZn_xS thin films were studied using EDX, SEM and X-ray diffraction techniques. The annealed films have been observed to possess a crystalline nature with a hexagonal structure. The optical absorption spectra were recorded within the range of 350-800 nm. The band gap of the as-deposited thin films varied from 2.46 to 2.62 eV, whereas in the annealed film these varied from 2.42 to 2.59 eV. The decreased band gap of the films after annealing was due to the improved crystalline nature of the material.     

Effect of sintering aid (CdCl2) on the optical and structural properties of CdZnS screen-printed film

Sulphides of zinc and cadmium have been utilized effectively in various opto-electronic devices. In the present work cadmium zinc sulphide (Cd_0.4Zn_0.6S) thin film has been deposited on ultra clean glass substrate by a simple inexpensive screen-printing method using cadmium sulphide, zinc sulphide, anhydrous cadmium chloride and ethylene glycol. Cadmium chloride has been used as sintering aid and ethylene glycol as a binder. Effect of sintering aid on the optical and structural properties of prepared cadmium zinc sulphide film has been investigated. The optical band gap (E_g) of the film has been studied by using reflection spectra in wavelength range 325–600 nm. It is found that reflection spectra suffer a drastic fall at two places, which is indicative of two band gaps of film viz. 2.38 eV and 2.9 eV corresponding to CdS and Cd_0.6Zn_0.4S, respectively. This is suggestive of the fact that cadmium zinc sulphide is a wide band gap semiconducting material. X-ray diffraction also confirms the formation of Cd_0.6Zn_0.4S composition.     

Microstructure,optical and structural characterization of Cd0.98Fe0.02S thin films co-doped with Zn by chemical bath deposition method

Fe-doped CdS (Cd_0.98Fe_0.02S) and Fe, Zn co-doped CdS (Cd_0.98−xZn_xFe_0.02S (x=0.02, 0.04, and 0.06)) thin films have been successfully deposited on glass substrate by chemical bath deposition technique using aqueous ammonia solution at pH = 9.5. Phase purity of the samples having cubic structure with (111) as the preferential orientation was confirmed by X-ray diffraction technique. Shift of X-ray diffraction peak position towards higher angle side and decrease of lattice parameters, volume and crystallite size confirmed the proper incorporation of Zn into Cd–Fe–S except Zn=6%. The compositional analysis (EDX) showed that Cd, Fe, Zn and S are present in the films. The enhanced band gap and higher transmittance observed in Cd_0.94Zn_0.04Fe_0.02S films are the effective way to use solar energy and enhance its photocatalytic activity under visible light. The enhanced green band emission than blue band by Zn-doping evidenced the existence of higher defect states.     

Microstructural, optical and photocatalytic properties of CdS doped TiO2 thin films

CdS doped TiO₂ thin films (with CdS content=0, 3, 6, 9 and 12 at%) were grown on glass substrates. The X-ray diffraction analysis revealed that the films are polycrystalline of monoclinic TiO₂ structure. The microstructure parameters of the films such as crystallite size (D_ν) and microstrain (e) are calculated. Both the crystallites size and the microstrain are decreased with increasing CdS content. The optical constants have been determined in terms of Murmann's exact equations. The refractive index and extinction coefficient are increased with increasing CdS content. The optical band gap is calculated in the strong absorption region. The possible optical transition in these films is found to be an allowed direct transition. The values of E_g^opt are found to decrease as the CdS content increased. The films with 3 at% CdS content have better decomposition efficiency than undoped TiO₂. The films with 6 at% and 9 at% CdS content have decomposition efficiency comparable to that of undoped TiO₂, although they have lower band gap. The CdS doped TiO₂ could have a better impact on the decomposing of organic wastes.     

Photoluminescence measurements in the phase transition region of Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>S films

Thin films of Zn_1−x Cd _x S (0.1 ≤ x ≤ 0.5) were prepared by using pulsed laser ablation technique on corning glass substrates. Phase transition from cubic to hexagonal in Zn_1−x Cd _x S films is determined by X-ray diffraction analysis. We observed a lowering in the phase transition temperature with increase in the cadmium concentration. Transmission electron microscopy suggests the crystalline nature of thin films with average particle size of 15 nm. The grown Zn_1−x Cd _x S samples show the high peak intensity ratio of the near band edge emission to the defect center luminescence even at room temperature, which indicates the small concentration of complex defects in the samples. Photoluminescence measurement show stoichiometric dependence of the energy band gap and is found to have quadratic dependence on x.     

Effect of indium doping in CdO thin films prepared by spray pyrolysis technique

Preparation of transparent and conducting indium doped CdO thin films by spray pyrolysis on glass substrate is reported for various concentration of indium (2-8 wt%) in the spray solution. The electrical, optical and structural properties of indium doped CdO films were investigated using different techniques such as Hall measurement, optical transmission, X-ray diffraction and scanning electron microscope. X-ray analysis shows that the undoped CdO films are preferentially orientated along (2 0 0) crystallographic direction. Increase of indium doping concentration increases the films packing density and reorient the crystallites along (1 1 1) plane. A minimum resistivity of 4.843×10⁻⁴ Ω cm and carrier concentration of 3.73×10²⁰ cm⁻³ with high transmittance in the range 300-1100 nm were achieved for 6 wt% indium doping. The band gap value increases with doping concentration and reaches a maximum of 2.72 eV for 6 wt% indium doping from 2.36 eV of that of undoped film. The minimum resistivity achieved in the present study is found to be the lowest among the reported values for In-doped CdO films prepared by spray pyrolysis method.     

Dielectric modelling of the transmittance spectra of thin As20S80 films

As₂₀S₈₀ thin films with different thicknesses (49.4-763.1 nm) were deposited on glass substrates using a thermal evaporation technique. Spectrophotometric measurements of the films' transmittance were taken in the wavelength range of 190-2500 nm. The transmission spectra were simulated with a computer model based on dielectric modelling to determine the optical constants and thicknesses of the films. The O'Leary-Johnson-Lim (OJL) models implemented in the commercial software programme SCOUT were used. Thicknesses obtained by the simulated method were correlated to the results obtained from a surface profiler technique. Optical parameters, such as the refractive index n, the absorption coefficient k, the optical band gap E_g, the high-frequency dielectric constant ε_∞, the Urbach energy E_U, the single-oscillator energy and the dispersion energy, were determined. The results indicated that the thickness effect can be separated into two distinct groups for films of thicknesses either less than or greater than 312 nm.     

Cerium (III) doping effects on optical and thermal properties of PVA films

Cerium chloride (CeCl₃) doped polyvinyl alcohol (PVA) films were prepared by casting technique. The effect of CeCl₃ concentrations on the structural, optical and thermal properties of the PVA films was studied by X-ray diffraction (XRD), FT-IR, UV-visible, transmittance (T), reflectance (R), differential scanning calorimetry (DSC) and thermogravimetry (TG). Both of the XRD and the DSC results affirm the increase in amorphousity. Absorption spectra of the doped films have shown an absorption band at 260 nm assigned to the trivalent state of cerium ions. Absorption, transmittance and reflectance spectra were used for the determination of the optical constants. The results indicate that the optical band gap (E_g) was derived from Tauc's extrapolation and decreases with the cerium content. The refractive index increases with monotonic behavior as the cerium content increases. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomernico model for obtaining the dispersion parameters. The obtained optical parameters were found to be strongly affected by CeCl₃ dopant. Thermal analysis showed that the thermal parameters of PVA are enhanced by CeCl₃. The dependence of the activation energy of the decomposition temperature on doping level was estimated.     

Optical,structural and magnetic properties of Zn0.9Cd0.1S:yCo nanoparticles

Zn_0.9Cd_0.1S:yCo nanoparticles were prepared by a co-precipitation method at low temperature. The obtained products were identified to be of cubic structure without any impurity phase. Cobalt incorporation leads to an increase in the local strain value and a decrease in the lattice constants as measured from XRD. Magnetic measurements showed that cobalt was incorporated in the Zn_0.9Cd_0.1S lattice as Co²⁺ and substituted for the Zn site as there was no evidence of the presence of metallic cobalt. Transmission electron microscopy suggests the crystalline nature of nanoparticles, with average particle size of ∼3.5 nm. UV-Vis measurements showed a red shift with respect to undoped nanoparticles in energy band gap with increasing cobalt concentration. Photoluminescence spectra reveal the defect-related emissions. The decay time constant is found to be in the nanosecond regime and is attributed to the spatial confinement of photo generated electron–hole pairs.     

Optical and electrical properties of In-doped CdO thin films fabricated by pulse laser deposition

Transparent indium-doped cadmium oxide (In-CdO) thin films were deposited on quartz glass substrates by pulse laser deposition (PLD) from ablating Cd-In metallic target at a fixed pressure 10 Pa and a fixed substrate temperature 300 °C. The influences of indium concentrations in target on the microstructure, optical and electrical performances were studied. When the indium concentration reaches to 3.9 wt%, the as-deposited In-CdO film shows high optical transmission in visible light region, obviously enhanced direct band gap energy (2.97 eV), higher carrier concentration and lower electric resistivity compared with the undoped CdO film, while a further increase of indium concentration to 5.6 wt% induces the formation of In₂O₃, which reverse the variation of these parameters and performance.     

Influence of indium content on the optical, electrical and crystallization kinetics of Se100−xInxthin films deposited by flash evaporation technique

Thin films of Se _100−xIn_x (x=10, 20 and 30 at%) have been prepared by the flash evaporation technique. The effect of the indium content on optical band gap of the Se_100−x In_x films has been investigated by the optical characterization. The optical band gap values of the Se_100−x In_x thin films were determined and are found to decrease with increasing indium content. This indium content changes the width of localized states in the optical band gaps of the thin films. It was found that the optical band gap, E_g, of the Se_100−x In_x films changes from 1.78 to 1.37 eV with increasing indium content from 10 to 30 at%, while the width of localized states in optical band gap changes from 375 to 342 meV. The temperature dependence of the dark electrical conductivity were studied in the temperature range 303-433 K and revealed two activation energies providing two electrical conduction mechanisms. The activation energy of the Se_100−x In_x films in the high temperature region changes from 0.49 to 0.32 eV with increasing indium content from 10 to 30 at%, while the hopping activation energy in the lower temperature region changes from 0.17 to 0.22 meV. The change in the electrical conductivity with time during the amorphous-to-crystalline transformation is recorded for amorphous Se_100−xIn_x films at two points of isothermal temperatures 370 and 400 K. The formal crystallization theory of Avrami has been used to calculate the kinetic parameters of crystallization.